1. Field of the Invention
The present invention generally relates to a dynamic aperture for controlling the intensity of light of projection lens, more particularly to a dynamic aperture driving apparatus and a method for reducing the vibration by which vibrations are minimized in spite of command for sudden location change.
2. Description of the Related Art
Recently, projection TVs and projectors are increasingly popular as a display device with a large, high-definition screen. The projection TV and projector are driven according to the principles of optics, and FIG. 1 is a diagram illustrating an optical structure of these kinds of projection TVs and projectors.
Referring to FIG. 1, a projection device comprises an illuminating optical system la, a reflection type display element 1b and a projection optical system 1c. 
The illuminating optical system 1a is a part that generates light, and comprises a lamp generating light (not illustrated), a light source 10 having a mirror to reflect the generated light and guide a path and an optical lens 20 to illuminate the incident light from the light source 10 to the reflection type display element 1b. 
The reflection type display element 1b reflects the incident light from the illuminating optical system 1a in units of pixels according to provided images, and comprises DMD (Digital Micromirror Device) 30, which is a projection type display device using semiconductors to control light. DMD 30 is mounted on a substrate 33 having a processor 31 and a memory 32, and divides the light path of an illuminating optical system 1a and one of the projection optical systems 1c corresponding to a tilt angle.
The projection optical system 1c projects the reflected images through the reflection type display element 1b on a screen 50, and comprises a projection lens module 40, enlarging the images transferred from DMD 30 and projecting on the screen 50.
Here, as illustrated in FIG. 2 the projection lens module 40 comprises a plurality of projection lenses 42, which are arrayed successively in a barrel 41 along the axis of light, and enlarges the incident images from DMD 30 in order to form clearly on the screen 50 spaced at a specific distance.
At this time, an aperture 43 to control the intensity of light is equipped within the plurality of projection lenses 42, and controls the intensity of light such that a projected image has a proper contrast ratio. At this time, for precisely controlling a contrast ratio, the location of the aperture 43 must be controlled in high resolving power having many steps in a certain arbitrary angle (30 degrees, for example). For a precise control of the location, a voice coil motor (hereinafter, VCM) 44 is typically used to rotate the aperture 43.
FIG. 3 is a diagram briefly illustrating a conventional dynamic aperture driving apparatus. Referring to FIG. 3, a conventional dynamic aperture driving apparatus comprises rotating means, driving means, sensing means and driving control means.
The rotating means comprises a pivot 111 which is embodied in one body with the aperture of the dynamic aperture driving apparatus 110 to rotate from one side to the other side in a given angle.
The driving means comprises a driving magnet 115 located on the rotation path of the other end of the pivot 111 and a driving coil 116 which is equipped in the lower end of the pivot 111 to face the driving magnet 115 and rotates the pivot 111 according to the magnitude of the driving current by the electro-magnetic effect with the driving magnet 115. Here, the driving means generally comes under VCM.
The sensing means comprises a sensor magnet 112 of providing different magnetic intensity according to each rotating angle of the pivot 111 and a hall sensor 113, rotating in one body with the pivot 111 and converting the magnetic intensity provided by the sensor magnet 112 to an electric signal.
The driving control means inputs a current to the driving coil 116, rotating the pivot 111, detects the present location of the pivot 111 through the sensor magnet 112 and the hall sensor 113, and feedback-controls the pivot 111 to move to the commanded location.
A dynamic aperture driving apparatus can additionally comprise a stopper 114 installed in the limit location of the rotating range of the pivot 111 to stop the pivot 111 that rotates over the critical value.
The process of detecting the location of dynamic aperture is as follows: As illustrated in FIG. 3, in the state that a current is not inputted in the driving coil 115, the rotating means 111 is in a stopped state by the stopper 114, and the output of the hall sensor 113 at this time is taken as a standard value. Then, as illustrated in FIG. 4, if the rotating means 111 rotates by an angle according to the commanded location, the output of the hall sensor 113 is changed, and the rotating angle of the rotating means 111 is calculated from the difference between the standard value in the stopped state and the present output of the hall sensor 113.
This dynamic aperture is usually equipped in an optical apparatus and controls the intensity of incident light. The operative principle is as follows: The dynamic aperture divides the range of light incident angle equally into 256 parts and controls the location from step 0 to step 255 based on the PWM duty signal corresponding to an image signal. Step 0 allows the least intensity of incident light by covering the most range of the incident light domain 100, as illustrated in FIG. 3, and step 255 allows the most intensity of incident light by covering the least range of the incident light domain 100, as illustrated in FIG. 4. The roles of step 0 and step 255 can also be reversed.
Meanwhile, as the conversion cycle of the PWM duty signal becomes shorter, the response time must respond to the speedier conversion. For example, in the case of displaying a lightning scene on the screen of a projection TV, the dynamic aperture must move back and forth between step 0 and step 255 in an extremely short time.
As the location changes in a very short time, a reverse current is flowed in the driving coil 116 and does breaking to allow a quick response with no overshoot. At this time, a maximum instant vibration occurs, and the generated vibration is converted to noise in the optical apparatus, which is a major shortcoming of a projection TV.